The country that suffers some of the world’s most powerful quakes has strict building codes, mandatory evacuations and emergency preparedness that sets a global example. But Chileans weren’t satisfied Wednesday, finding room for improvement. Experts warn that a “seismic gap” has left Chile overdue for a far bigger quake.

Authorities on Wednesday discovered six reported deaths from the Tuesday night’s quake. It’s possible that other people were killed in older structures made of adobe in remote communities that weren’t immediately accessible, but it’s still a very low toll for such a powerful shift in the undersea fault that runs along the length of South America’s Pacific coast.

“How much is it luck? How much is it science? How much is it preparedness? It is a combination of all of the above. I think what we just saw here is pure luck. Mostly, it is luck that the tsunami was not bigger and that it hit a fairly isolated area of Chile,” said Costas Synolakis, an engineer who directs the Tsunami Research Center at the University of Southern California.

The U.S. Geological Survey said a powerful 7.8-magnitude aftershock hit Chile’s far-northern coast Wednesday night, shaking the same area where the 8.2 earthquake hit just a day earlier.

The Wednesday tremor caused buildings to shake in the port of Iquique. There were no immediate reports of new damage or injuries. The tremor came 45 minutes after a strong 6.4-magnitude aftershock.

Chile is one of the world’s most seismic countries and is prone to tsunamis because of the way the Nazca tectonic plate plunges beneath the South American plate, pushing the towering Andes cordillera ever higher.

About 2,500 homes were damaged in Alto Hospicio, a poor neighborhood in the hills above Iquique, a city of nearly 200,000 people whose coastal residents joined a mandatory evacuation ahead of a tsunami that rose to only 8 feet. Iquique’s fishermen poked through the aftermath: sunken and damaged boats that could cost millions of dollars to repair and replace.

The shaking that began at 8:46 p.m. Tuesday touched off landslides that blocked roads, knocked out power for thousands, briefly closed regional airports and started fires that destroyed several businesses. Some homes made of adobe were destroyed in Arica, another city close to the quake’s offshore epicenter.

And seismologists warn that the same region is long overdue for an even bigger quake.

“Could be tomorrow, could be in 50 years; we do not know when it’s going to occur. But the key point here is that this magnitude-8.2 is not the large earthquake that we were expecting for this area. We’re actually still expecting potentially an even larger earthquake,” said Mark Simons, a geophysicist at the California Institute of Technology.

Nowhere along the fault is the pressure greater than in the “Iquique seismic gap” of northern Chile. “This is the one remaining gap that hasn’t had an earthquake in the last 140 years,” Simons said.

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